Dynamoelectric machines such as electric motors, alternators and the like are typically constructed with an annular stator within which a rotating field is rotatably mounted. The stator construction typically includes an annular magnetic core having circumferentially distributed and axially extending stator slots. The stator winding consists of coils spanning the distance of a pole pitch and interconnected together to form groups in accordance with the phase connection.
In some instances, it is advantageous for the stator to be internally positioned relative to an external rotor. For example, U.S. Pat. No. 5,355,039 entitled “ELECTRICLALY MOTORIZED WHEEL ASSEMBLY” issued on Oct. 7, 1994 to Couture describes a rotor-wheel having an external rotor.
Two basically different winding techniques are employed in the manufacture of dynamoelectric machines. In the first winding technique, the particular coil is wound and formed in place in the associated magnetic core. Typically one, or occasionally more than one, relatively flexible conductors are serially led down one core slot in one axial direction, and back in the other axial direction through another core slot a plurality of times, usually by machine to fabricate a coil having a predetermined number of conductor turns. Alternatively, the coil of flexible conductors is wound first around a bobbin to provide a desired coil which is thereafter formed in place in the core slots to provide a machine winding.
The essential attribute of such a first winding technique is that the individual conductors are flexible, like a balling wire, and while the coil so formed may be a compact bundle of conductors, yet the coil itself is readily deformable since the individual conductor strands act essentially independently in the sense that relative movement between conductors is restrained chiefly only by surface friction among adjacent conductors.
The conductors in such winding are typically wound copper or aluminum wires having a thin resinous film or serving of insulating material to provide what is commonly called magnet wire. The machines having windings in accordance with this first technique are oftentimes characterised as “mush” or “random” wound machines.
In some situations, because of insulation requirements or other constraints, it is desirable to resort to the second winding technique using so-called “formed” coils. In this second technique, the coils are pre-formed prior to insertion in the core slots and the machines so constructed are frequently characterised as “formed wound machines”. The conductors in the typical formed coils are bars or strips having a substantially rectangular cross-section of copper or aluminum which carry a conductor insulation usually in the form of a plurality of layers of fabric, micaceous material and/or resinous compositions.
After a coil is wound with such conductors, it is thereafter covered with coil insulation that binds the conductors together and severely restricts any relative motion therebetween thereafter. Thus, the “formed” coil is typically a substantially rigid structure relative to the typical “random” coil that does not employ such coil insulation.
An example of a typical “formed wound machine” is disclosed in U.S. Pat. No. 5,714,825 entitled “CONDUCTOR SECTION FOR A STATOR FRAME OF A POLYPHASE DYNAMOELECTRIC MACHINE” issued on Feb. 3, 1998 to Couture et al. This patent discloses a conductor section made of two parallel and generally rectangular conductors provided with a generally U-shaped head interconnecting the two conductors. The stator slots of such “formed wound machines” are typically rectangular in cross-section.
A common problem associated with the manufacture of such “formed wound machines” is related to the difficulty of inserting the pre-formed coils or windings in the stator slots without distorting or deforming the coils so as to reduce the risks of damaging the insulation thereof and potentially causing short circuits or the like. The problem is compounded in situations, such as exemplified by U.S. Pat. No. 5,714,824, wherein the stator is internal, having stator slots that project outwardly and, therefore, radially fan outwardly. Indeed, the radially outward opening of two slots being at a greater distance than the radially inwardly located opening of the same two slots, insertion of conventional pre-formed coils inherently requires at least temporary deformation thereof.
Accordingly, there exists a need for an improved dynamoelectric machine stator and an improved method for mounting pre-wound coils thereunto.